Enzymatic nitration of phytophenolics: evidence for peroxynitrite‐independent nitration of plant secondary metabolites

摘要

>Peroxynitrite (ONOO−), a reactive nitrogen species, is capable of nitrating tyrosine residue of proteins. Here we show in vitro evidence that plant phenolic compounds can also be nitrated by an ONOO−-independent mechanism. In the presence of NaNO₂, H₂O₂, and horseradish peroxidase (HRP), monophenolic p-coumaric acid (p-CA, 4-hydroxycinnamic acid) was nitrated to form 4-hydroxy-3-nitrocinnamic acid. The reaction was completely inhibited by KCN, an inhibitor for HRP. The antioxidant ascorbate suppressed p-CA nitration and its suppression time depended strongly on ascorbate concentration. We conclude that nitrogen dioxide radical (NO₂ • ), but not ONOO−, produced by a guaiacol peroxidase is the intermediate for phytophenolic nitration.